Resolves conflicts between reverts of pattern library test pages and multi-site comprehensive theming, and the re-introduction of pattern library test pages. Fixes a pipeline rendering test which relied on other tests updating assets. The test now ensures that static assets are available before running.

FEDX-93

These are developer only pages, so can not be seen in production
environment. On devstack, you can access these pages in LMS and
Studio at:

    /template/ux/reference/pattern-library-test.html

This is the second attempt to enable the Pattern Library. The
first attempt broke Django Templates and didn't work correctly
with right-to-left styling.

This reverts commit 845e3708.

This reverts commit 845e3708.

FEDX-93

These are developer only pages, so can not be seen in production
environment. On devstack, you can access these pages in LMS and
Studio at:

    /template/ux/reference/pattern-library-test.html